Lightweight mirrors are needed for a wide variety of applications, for example, in the space and aeronautics industries. Particularly in space and aeronautics applications, it is important to reduce the overall weight of the system. It is also important to produce precise optical components.
U.S. Pat. No. 7,145,739 issued on Dec. 5, 2006 and is entitled “Lightweight Optical Mirrors Formed in Single Crystal Substrate.” The entire contents of U.S. Pat. No. 7,145,739 are expressly incorporated by reference herein. The '739 patent discloses lightweight optical mirrors formed in a single crystal substrate. Mirrors made by the '739 process may be high quality. According to the '739 process, a mirror surface is polished, and then ultrasonic machining is used to light weight the mirror. But, ultrasonic machining is a relatively time-consuming and expensive machining process.
The modest removal rate of ultrasonic machining may be a problem for larger mirrors because the volume of material to be removed by ultrasonic machining increases as the cube of the mirror diameter. Also, because ultrasonic machining depends on a working fluid, and the surface to volume ratio may change with mirror size, the design of the ultrasonic tool may need to be re-optimized as the size of the mirror increases.
A need exists for a less expensive method of making high quality, lightweight mirrors from a single crystal substrate.